Electrical contact materials are supposed to transmit electric currents as far as possible without losses and safely. This current conduction takes place through interfaces for which a metallic conduction mechanism cannot be assumed in all cases. Specifically, there are then possibilities for charge transfer both by virtue of semiconductor effects in non-metallic covering layers and by virtue of any gas discharge mechanisms in the open contact gap. From a pure design perspective, the following demands may be imposed on such conductive connections between different components:
1. The connection should be permanent, and can accordingly be made by purely mechanical means, such as screw or clamp connections or spring elements, or by metallurgical measures, such as welding or soldering.
2. The connection should only be made at discrete time intervals. The components are then described as interrupter or breaker contacts. Among these contacts, a distinction needs to be drawn between the groups of contacts which switch without current and the group of contacts in which there is a flow of current during the switching operation.
3. The connection is to be made between components which are used to transmit a flow of current while they are moving relative to one another. The components are then referred to as rubbing or sliding contacts.
Currently, it is primarily copper-based alloys comprising two or more substances which are used for these applications. What are known as beryllium bronzes, i.e. technical-grade copper alloys containing, for example, 1.2, 1.7 and 2.0% by weight of beryllium, are in widespread use. These alloys have very good hot age-hardening properties and in terms of their ratio of strength to deformability and to conductivity are among the highest quality copper-based electrical contact materials currently available. In addition to the abovementioned binary beryllium bronzes, ternary beryllium bronzes with beryllium contents of less than 1% by weight and additions of up to 3% by weight of nickel or cobalt are also commercially available. A large proportion of these materials are used in the as-produced heat-treated state, i.e. the heat treatment is carried out by the manufacturer of the alloy.
On account of the increasingly strict regulations on electrical scrap throughout the world, electrical scraps have to be disposed of as special waste. Consequently, beryllium bronzes will become much more expensive in the near future, since the toxic effect of beryllium means that their disposal costs are relatively high.